Default button inside UpdatePanel

I have UpdatePanel with grids, textboxes and buttons inside it.  there are three buttons  positioned in order : btn01, btn02, btn03...

Every time text box recdieving focus ( attempt to start typing) btn01 became default button, means if enter hit, postback starts as btn01 would be clicked.  That is something that I need to prevent from happening.  One of the way is to position btn03 as first button on the page then it will become 'defaultbutton' and when enter hit postback get initiates as btn03 get clicked.  I'm looking for the way to do the following :

1. Without changing physical order of the buttons set default buttoon to btn03. Can not fing property/dynamic way  to do so.

2. Disable defaultbutton at all, so if during entering text into text box 'enter' key hit - nothing happening ( no postback )

Thanks